I. Field of the Invention
The present invention relates to mobile systems carrying rotatable mixing drums for mixing charged ingredient materials and dispensing concrete. More specifically, this invention relates to a helical mixing fin assembly for mixing and moving materials within concrete mixing drums that involves a fin design structure that provides superior mixing of the charged ingredient materials within rotatable drum mixers.
II. Related Art
Concrete mixing trucks are widely used in the construction industry for preparing and transporting concrete mix to desired construction sites. Such trucks feature a large rotatable mixing drum which includes fins or agitators mounted inside for mixing and directing the movement of a concrete mixture therein. Such fins typically have a helical configuration which will tend to mix concrete ingredients when the mixing drum is rotated in a first direction and urge the concrete towards a discharge chute when the mixing drum is turned in an opposite direction.
The mixing or agitation of materials such as concrete in a rotary mixing environment creates a great deal of abrasive friction between the mixing fins, and the interior surface of the drum, with the various abrasive components of the concrete mixture which is being transported. The mixing fins themselves have also typically been constructed of heavy metal plate stock which may be polymer-coated or they may be constructed of a polymeric stock. Mixing fins have even been provided with small mixing holes to aid in blending materials. Such a fin system is shown in U.S. Pat. No. 8,646,965 B2 to Datema et al. However, the very small holes in rather large fins have been found to provide only a very limited benefit and the fins still inhibit any free flow of materials along the drum.
In addition prior fin systems have consisted of a large number of rather short conjoined sections which require a great deal of labor to assembly in the mixing drum. Dual spiral mixing fin structures are also known. A dual spiral mixing fin structure is shown, for example, in U.S. Pat. No. 5,056,924 to Christenson. That type of design is further illustrated in FIGS. 1 and 2.
FIG. 1 is a side elevational view of a mobile system for mixing and dispensing concrete with a portion of the mixing drum wall cut away to expose the fins. The mobile system includes a mixing truck 10 having a cab portion 12 and a rear portion 14 which has a main frame 16. A mixing drum 18 is mounted for rotation on a front support frame 20 and a rear support frame 22, both of which are integral with the main frame 16. A rearward portion of the mixing drum 18 is positioned adjacent a discharge mechanism 24 which includes a funnel for charging concrete components into the mixing drum 18, as well as a portion for discharging mixed concrete into a main chute 26, as is well known in the art. Main chute 26 is supported relative to rear support frame 22 by a pivot joint 28 which, in turn, enables main chute 26 to be positioned over a set of forms or other desired location for use of the mixed concrete. As may be seen in FIGS. 1 and 2, mixing drum 18 includes a front head cone 31 and front cone 30, a belly or crossover portion 32, a big cone portion 34 and a rear tail cone portion 35 which terminates at the end of truck 10 and which is proximate the discharge mechanism 24, which is supported by rear support frame 22. A conventional dual helical or spiral mixing fin assembly 36 is mounted to an inner surface of an outer wall and extends transversely into the mixing space of mixing drum 18.
The fin assembly 36 includes a first rearwardly curving segment 37, a second forwardly curved fin segment 39 and a transitional fin portion 41 which connects the rearwardly curving segment 37 and the forwardly curving segment 39. As can be seen from the figures, a concrete mixture will be agitated by the fin segments 37, 39 and 41 when mixing drum 18 is caused to rotate in a first direction, while the fin segments will urge the mixture toward the discharge mechanism 24 when the rotational direction of the mixing drum 18 is reversed. The forward curving fin segment 39 acts to help lift and toss the mixture toward the middle of the drum 18 when the drum 18 is rotated to mix the material. The various sections of spiral fin assembly 36 are secured in the mixing drum 18 in a conventional manner.
As can be seen, particularly in FIG. 1, concrete mixing drums of conventional design have had a mixing fin assembly 36 which forms spiral mixing flights located symmetrically opposite and rotated 180° apart. The two flights are usually identical to each other in most conventional designs, especially in the discharge portion. As stated, the rotation of the drum in a given direction allows material to be loaded into the drum and agitated, while rotation of the drum in the opposite direction will discharge the concrete as it slides off the flighting toward the outlet end.
A long standing problem in the art of concrete drum mixing technology has been associated with the forward and rearward migration of the materials during the mixing and discharge processes. The material must move up and over the mixing fins as it moves forward or aft in the drum this causes increased wear to both the mixing fins and the drum inner wall. The solid fins also present an impediment to the drum clean out process and the removal of residual concrete after use.